This invention relates to the manufacture of substrates for magnetic disks.
It is known in the art to use glass as a substrate material to manufacture magnetic disks. During substrate manufacturing, disk-shaped substrates are cut out of a sheet or square of glass. This is typically accomplished by providing a sheet 1 of glass (FIG. 1), and cutting sheet 1 into squares 2 of glass. Thereafter, glass substrates 3 are cut out of squares 2. Glass is typically cut by scribing and breaking. (Scribing is accomplished using either diamond or laser scribing. The scribe marks are shown in FIG. 1 as dotted lines.) During scribing, glass square 2 is mounted on an x-y stage, which moves square 2 against a diamond scribing instrument for the case of diamond scribing. For the case of laser scribing, the x-y stage moves glass square 2 while a laser beam is directed toward the glass. After scribing, the glass is broken along the scribe line. As can be seen, two sets of scribe lines must be formed on square 2xe2x80x94an inner diameter scribe line 4 and an outer diameter scribe line 5. For magnetic disk applications, scribe lines 4 and 5 must be circular, concentric, and precisely positioned. Unfortunately, there are several problems with this manufacturing method.
1. It is difficult to achieve good concentricity with an x-y stage.
2. It is difficult to achieve precise control over the motion of the x-y stage as it moves in a circle. (X-y stages achieve a positional tolerance of about 60 xcexcm, which is outside the requirements for most magnetic disk applications.)
3. X-y stages are slow.
Another problem with this scribing method is that during breaking, the resulting edge of the glass substrate is jagged. This is due in part to the fact that although the glass break line starts at the scribe line, the break line will tend to form between defects or weak regions in the glass. FIG. 2 illustrates in cross section glass square 2 and a break line 6 resulting from scribing and breaking square 2. Referring to FIG. 2, although break line 6 starts at scribe line 5, break line 6 follows a jagged path, typically extending between scribe line 5 and defects such as defect 7. The result is that the edge of the substrate is poorly defined, jagged and sharp. To remedy this situation, the substrate must be subjected to expensive edge polishing processes.
A method for cutting a workpiece in accordance with one embodiment of the invention comprises mounting the workpiece on a rotating spindle, and scribing the workpiece while it is rotating. Advantageously, the workpiece can be scribed more rapidly using this technique than if an x-y stage were employed. Further, the position of the scribe line can be more precisely controlled than if an x-y stage were employed.
In one embodiment, the workpiece is formed into a substrate for use in magnetic disk manufacturing. The inner and outer diameters of the substrate are formed by scribing using the above-mentioned rotating spindle. It is easier to scribe inner and outer diameter scribe lines, and to maintain concentricity of these scribe lines, using the above-mentioned spindle than if an x-y stage were employed.
In one embodiment, both inner and outer diameter scribe lines are scribed simultaneously. This increases throughput, and reduces manufacturing expense.
In accordance with a second embodiment of the invention, both sides of a workpiece are scribed simultaneously. Because scribe lines are formed on both sides of the workpiece, the resulting break line will extend between the scribe line on one side of the workpiece and the scribe line on the other side of the workpiece. The resulting scribe line is less jagged and better defined than if only one side of the workpiece was scribed. Because both sides of the workpiece are scribed simultaneously, throughput is increased.
In one embodiment, the workpiece is mechanically scribed. In another embodiment, the workpiece is scribed using a radiant energy source such as a laser and then broken along the laser-induced scribe line. In another embodiment, after subjecting the workpiece to laser scribing, the workpiece is etched. The portion of the workpiece exposed to the laser etches more rapidly than the portions of the workpiece that have not been exposed to the laser. Accordingly, grooves are formed at the locations where the workpiece has been etched. These grooves serve as scribe lines to help initiate the crack and provide a smooth workpiece edge after breaking.
In one embodiment, the workpiece is glass or glass ceramic. However, the workpiece can be other materials as well. Brittle materials are particularly suited to this method.